Copolymers of ethylene and acrylate esters have been reported in the literature, such as in U.S. Pat. No. 3,350,372, issued Oct. 31, 1967 to Anspon et al. This patent discloses ethylene-acrylate ester copolymers wherein the acrylate esters include, for example, methyl acrylate, 2-butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, octadecyl acrylate and the corresponding esters of methacrylic acid.
U.S. Pat. No. 3,756,996, issued Sep. 4, 1973 to D. W. Pugh et al., which is hereby incorporated by reference in its entirety, discloses an apparatus and method for polymerizing ethylene and other monomers in a multi-zoned reactor system.
U.S. Pat. No. 4,351,931, issued Sep. 28, 1982 to Armitage, discloses high molecular weight, uniformly random copolymers of ethylene and acrylic or methacrylic acid which are made by maintaining a definite and constant ratio of acrylic acid to ethylene in a continuous-feed autoclave reactor having good mixing which maintains uniformity of the mixture throughout the entire reactor. These copolymers are limited to 10 wt % of the acid in order to provide improved handling and adhesive qualities.
The copolymerization of ethylene and an alkyl acrylate monomer (such as methyl acrylate) in a high-pressure autoclave reactor typically produces a copolymer resin, such as ethylene-methyl acrylate copolymer ("EMAC"), having a given alkyl acrylate content and a given melt-point temperature. The melt-point temperature of these copolymers has limited their use to those applications where the temperature of the article containing the copolymer remains safely below the melt-point temperature of the copolymer. A higher melt-point temperature for such copolymers, without affecting other properties such as the flexural stiffness and the adhesive properties of the copolymer, would allow their use in higher temperature applications. The present invention provides ethylene-alkyl acrylate copolymers with higher melt-point temperatures and processes for preparing them.